Close inspection by scuba diving revealed that the structure is made of basalt boulders up to 1 meter long with no apparent construction pattern and no signs of cutting or chiseling.

"A possible interpretation for the structure is related to the fact that it attracts fish and thus may be interpreted as a part of a marine-based economy. If so, the structure must have been built as an underwater structure," the archaeologists wrote, noting that structures built of stone that are thought to be ancient fish nurseries are well known in the Sea of Galilee and are found near the shores at regular intervals. However, they are significantly smaller than the structure revealed recently, with diameters of up to 4 meters.

An alternative scenario is that the structure was built onshore, when the water level was lower than today.

A report on LiveScience.com said the structure appears to be a giant cairn, with rocks piled on top of each other. "Structures like this are known from elsewhere in the world and are sometimes used to mark burials," according to the report. "Researchers do not know if the newly discovered structure was used for this purpose."

Researcher Yitzhak Paz, of the Israel Antiquities Authority and Ben-Gurion University, told LiveScience.com the structure could date back more than 4,000 years. The "effort invested in such an enterprise is indicative of a complex, well-organized society, with planning skills and economic ability," the researchers wrote in their journal paper.